Développement et validation de méthodes dosimétriques en ligne pour le traitement du cancer de la prostate

Currently, the treatment of prostate cancer under open MRI at the University of Geneva Hospital, applying high dose rate (HDR) brachytherapy, involves three main steps : needle implantation, dosimetric calculations and irradiation. As such, there is no pre-planning of the treatment, the experience of the physician providing the sole basis for deciding upon the number and position of the needles. Moreover, since the implantation and the dosimetry are performed at different places and at different times, it is not possible to modify the needle configuration, in case it is found that the entire tumour volume cannot be sufficiently irradiated. The present research aims at achieving a significant improvement of the cancer treatment by introducing new methods for HDR brachytherapy involving inverse planning procedures and three dimensional dosimetric databases. Thereby, the possibility is offered to the radio-oncologist to define the regions to be treated, to express the desired values for the dose to be imposed or tolerated for each organ, to propose a specific needle configuration and to verify the relevance of the proposition before proceeding to implantation. Finally, a guiding system, coupled to the MR imaging, serves to ensure correspondence between virtual and real treatment. Such possibilities require the development and validation of appropriate routines for dosimetric calculations and the accurate and rapid optimisation of irradiation conditions, for various source types, both gamma and beta emitting. The final product of the present research is a programme called PROTON. Other necessary developments, which are being implemented by a collaborating organisation, viz. the Signal Processing Laboratory at EPFL, concern the graphical interface of the programme, the volume segmentation tools and the implantation guidance. The dosimetric problem is solved by applying detailed Monte Carlo simulations to generate 3-dimensional databases, which are large enough in extent to cover a standard treatment volume with a single source placed at its centre. The dose map corresponding to location of several sources can then be obtained via a linear combination of dose values from the database of the specific source. The chosen sources for the simulations are the 192Ir model microSelectron of Nucletron B. V., two HDR prototypes with 169Yb and 144Ce and the LDR implants 6711 with 1251 from OncoSeed and 200 with 103Pd from TheraSeed. The next step taken is to verify the accuracy and pertinence of the databases, via experimental studies involving a single source and by comparisons with numerical results obtained applying other methods. The experimental verification carried out has been for the 192Ir and 144Ce sources. Radial dose rate distributions were measured in a water phantom employing accurately calibrated detectors of several different types, both active and passive. For 192Ir, a 0.22 cm3 ionisation chamber, cylindrical lithium fluoride thermoluminescent dos